IT PRO has published a great list of top tips for GreenIT. Interestingly, most should help towards day-to-day cost saving too

1. Teleconferencing
2. Ditch Paper
3. E-documents and online tools
4. Consolidated data centres
5. Virtualisation
6. Home Working
7. Server rooms
8. Desktop rooms and the grid
9. Turn it off
10. Think holistically

Full details here